I've recently started using Calibre on an Ubuntu system, and am generally pretty happy with it.

I heavily use Gnome Do on the desktop for searches, etc. and know that there is a rather nice plugin for Rhythmbox with it. It occurs to me that it would be nice to have a Calibre plugin for searches in Gnome Do.

I don't have an answer to your question, but just throwing out there that I also just installed Calibre on Ubuntu Linux last night and love it! I'll hopefully have a Kindle 3 on order very soon, so I'm getting my book collection cleaned up before importing it over.